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Abstract:

A catalyst for use in the production of an unsaturated aldehyde and/or an
unsaturated carboxylic acid, the catalyst comparing (or, preferably,
being composed of) a mixed oxide containing molybdenum, bismuth and iron,
which has improved methanical strength, is produced by a method including
the steps of (1) drying an aqueous solution or an aqueous slurry
containing raw materials of the catalyst and then firstly calcining a
dried product in a molecular oxygen-containing gas atmosphere to obtain a
calcined product; (2) heating the calcined product obtained in Step (1)
in the presence of a reducing material to obtain a reduced product having
a mass loss of 0.05 to 6%; and (3) secondly calcining the reduced product
obtained in Step (2) in a molecular oxygen-containing gas atmosphere.

Claims:

1. A method for producing an unsaturated aldehyde and/or an unsaturated
carboxylic acid, comprising the steps of: (i) producing a catalyst
comprising a mixed oxide comprising molybdenum, bismuth and iron by a
method comprising the steps of: (1) drying an aqueous solution or an
aqueous slurry containing raw materials of the catalyst and then
calcining a dried product in a molecular oxygen-containing gas atmosphere
to obtain a calcined product; (2) heating the calcined product obtained
in Step (1) in the presence of a reducing material to obtain a reduced
product having a mass loss, represented by the following equation (I), of
0.05 to 6%: Mass loss(%)=[(Wa-Wb)/Wa]×100 (I) in which Wa is a
weight of a calcined product before the reduction treatment, and Wb is a
weight of a reduced product after the reduction treatment; and (3)
calcining the reduced product obtained in Step (2) in a molecular
oxygen-containing gas atmosphere, and (ii) a gas phase catalytic
oxidation of at least one compound selected from the group consisting of
propylene, isobutylene and tert-butyl alcohol with molecular oxygen in
the presence of the catalyst produced in step (i).

Description:

[0001] This application is a Divisional of co-pending application Ser. No.
12/467,079, filed on May 15, 2009, which claims priority under 35 U.S.C
§119(a) to Patent Application No. 2008-129200 filed in Japan on May
16, 2008, all of which are hereby expressly incorporated by reference
into the present application and for which priority is claimed under 35
U.S.C. §120.

FIELD OF THE INVENTION

[0002] The present invention relates to a method for producing a catalyst
for use in the production of an unsaturated aldehyde and/or an
unsaturated carboxylic acid. The present invention also relates to a
method for producing an unsaturated aldehyde and/or an unsaturated
carboxylic acid by using a catalyst prepared by the foregoing method.

DESCRIPTION OF PRIOR ART

[0003] A catalyst composed of a mixed oxide comprising molybdenum, bismuth
and iron is effective as a catalyst to be used for producing acrolein
and/or acrylic acid by a gas phase catalytic oxidation of propylene with
molecular oxygen, and also effective as a catalyst to be used for
producing methacrolein and/or methacrylic acid by a gas phase catalytic
oxidation of isobutylene or tert-butyl alcohol with molecular oxygen. It
is known that such a catalyst is prepared generally by drying an aqueous
solution or an aqueous slurry containing catalyst components and then
calcining the dried product. In the use of this type of catalyst for the
above oxidation reactions, the catalyst is filled in the form of a molded
catalyst or a supported catalyst in a fixed bed reactor. If the catalyst
has low mechanical strength, it tends to be broken when it is filled in a
reactor and, as a result, a pressure drop occurs in the reactor during
the reaction. Therefore, such a catalyst is required to have high
mechanical strength.

[0004] To increase the mechanical strength of a catalyst, the compounding
of inorganic fiber in a catalyst during the preparation thereof is
proposed (see JP-A-06-000381, JP-A-2002-273229 and JP-A-09-052053).

[0005] However, a catalyst prepared by the above method may not
necessarily have satisfactory mechanical strength.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide a method for
producing a catalyst for use in the production of an unsaturated aldehyde
and/or an unsaturated carboxylic acid, which catalyst comprises a mixed
oxide comprising molybdenum, bismuth and iron and has improved mechanical
strength.

[0007] As the result of extensive studies by the present inventors, it has
been found that the above object can be accomplished when a catalyst for
use in the production of an unsaturated aldehyde and/or an unsaturated
carboxylic acid, the catalyst comprising (or, preferably, being composed
of) a mixed oxide containing molybdenum, bismuth and iron, is used which
is produced by a method comprising Step (1), (2) and (3) described below.

[0008] Thus, the present invention provides a method for producing a
catalyst for use in the production of an unsaturated aldehyde and/or an
unsaturated carboxylic acid, the catalyst comprising (or, preferably,
being composed of) a mixed oxide comprising molybdenum, bismuth and iron,
said method comprising the steps of

[0009] (1) drying an aqueous solution or an aqueous slurry containing raw
materials of the catalyst and then firstly calcining a dried product in a
molecular oxygen-containing gas atmosphere to obtain a calcined product;

[0010] (2) heating the calcined product obtained in Step (1) in the
presence of a reducing material to obtain a reduced product having a mass
loss, represented by the following equation (I), of 0.05 to 6%;

Mass loss(%)=[(Wa-Wb)/Wa]×100 (I)

in which Wa is a weight of a calcined product before the reduction
treatment, and Wb is a weight of a reduced product after the reduction
treatment; and

[0012] Furthermore, the present invention provides a method for producing
an unsaturated aldehyde and/or an unsaturated carboxylic acid comprising
the steps of

[0013] producing a catalyst by the method for the production of the
catalyst according to the present invention, and

[0014] a gas phase catalytic oxidation of at least one compound selected
from the group consisting of propylene, isobutylene and tert-butyl
alcohol with molecular oxygen in the presence of the catalyst produced in
the above step.

[0015] The method of the present invention can provide a catalyst having
better mechanical strength for use in the production of an unsaturated
aldehyde and/or an unsaturated carboxylic acid. Moreover, when the
catalyst produced by the method of the present invention is used in the
production of an unsaturated aldehyde and/or an unsaturated carboxylic
acid, the breakage of the catalyst is well prevented during filling it in
a reactor. As a result, it is possible to reduce the pressure drop during
the reaction and to catalytically oxidize a compound selected from the
group consisting of propylene, isobutylene and tert-butyl alcohol stably
with molecular oxygen in a vapor phase to produce an unsaturated aldehyde
and/or an unsaturated carboxylic acid.

DETAILED DESCRIPTION ON THE INVENTION

[0016] The catalyst for use in the production of an unsaturated aldehyde
and/or an unsaturated carboxylic acid according to the present invention
comprises (or, preferably, is composed of) a mixed oxide comprising
molybdenum, bismuth and iron as the essential elements. The mixed oxide
may optionally contain at least one element other than molybdenum,
bismuth and iron. For example, the mixed oxide may preferably contain at
lease one element selected from the group consisting of nickel, cobalt,
potassium, rubidium, cesium and thallium.

[0017] A preferable example of such a mixed oxide is a compound
represented by the following formula (II):

MoaBibFe.sub.cAdBeC.sub.fDgOx (II)

wherein Mo, Bi and Fe represent molybdenum, bismuth and iron,
respectively, A represents nickel and/or cobalt, B represents an element
selected from the group consisting of manganese, zinc, calcium,
magnesium, tin and lead, C represents an element selected from the group
consisting of phosphorus, boron, arsenic, tellurium, tungsten, antimony,
silicon, aluminum, titanium, zirconium and cerium, D represents an
element selected from the group consisting of potassium, rubidium, cesium
and thallium, O represents oxygen, a, b, c, d, e, f and g satisfy the
following relationships: 0≦b≦10, 0≦c≦10,
1≦d≦10, 0≦e≦10, 0≦f≦10 and
0≦g≦2, when a is set equal to 12, and x is a value
determined depending upon the oxidation states of the other elements. For
example, x may be determined by multiplying the valence of each element
(except for oxygen) comprised in the mixed oxide with its corresponding
stoichiometric proportion within the mixed oxide, and adding up the
multiplication products to form a sum, whereby the sum thus formed
divided by 2 equals x. Accordingly, if the mixed oxide is, for example,
Mo12Bi5Fe4Co10CsOx and the valences of Mo, Bi,
Fe, Co and Cs in this compound are VI, III, III, II and I, respectively,
x can be determined by the above method as
x=[(126)+(35)+(34)+(210)+(11)]/2=60 (i.e., the mixed oxide would have the
formula Mo12Bi5Fe4Co10CsO60).

[0018] Among the compounds represented by formula (II), those having the
following compositions (except for oxygen atoms) are preferably used:

[0019] Mo12Bi0.1-5Fe0.5-5Co5-10Cs0.01-1

[0020] Mo12Bi0.1-5Fe0.5-5Co5-10Sb0.1-5K0.01--
1

[0021] Mo12Bi0.1-5Fe0.5-5Ni5-10Sb0.1-5Si0.1--
5Tl0.01-1

[0022] Hereinafter, a method for producing the catalyst according to the
present invention is explained. An aqueous solution or an aqueous slurry
containing raw materials of the catalyst is dried and then, the dried
product is calcined firstly in a molecular oxygen-containing gas
atmosphere [Step (1)]. As the raw materials of the catalyst, in general,
compounds of the respective elements constituting the catalyst, such as
oxides, nitrates, sulfates, carbonates, hydroxides, oxoacids and ammonium
salts thereof, and halides, are used in ratios such that desired atomic
ratios of the elements are satisfied. For example, molybdenum trioxide,
molybdic acid, ammonium paramolybdate and the like may be used as a
molybdenum compound. Bismuth oxide, bismuth nitrate, bismuth sulfate and
the like may be used as a bismuth compound. Iron (III) nitrate, iron
(III) sulfate, iron (III) chloride and the like may be used as an iron
compound. Cobalt nitrate, cobalt sulfate, cobalt chloride and the like
may be used as a cobalt compound. Antimony trioxide, antimony (III)
chloride and the like may be used as an antimony compound. Cesium
nitrate, cesium carbonate, cesium hydroxide and the like may be used as a
cesium compound.

[0023] The aqueous solution or the aqueous slurry containing the raw
materials may be prepared by mixing the raw materials with water. A
mixing temperature and an amount of water used may adequately be
selected. The aqueous solution or the aqueous slurry may be dried using a
kneader, a box dryer, a drum-type through-air dryer, a spray dryer, a
flush dryer, or the like.

[0024] The dried product obtained by the above drying step is firstly
calcined (first calcination) in the molecular oxygen-containing gas
atmosphere. The concentration of molecular oxygen in the molecular
oxygen-containing gas is usually from 1 to 30% by volume, and preferably
from 10 to 25% by volume. Ambient air or pure oxygen is usually used as
the source of molecular oxygen. Such a source is used as a molecular
oxygen-containing gas, if necessary, after being diluted with nitrogen,
carbon dioxide, water, helium, argon, or the like. A calcination
temperature in the first calcination step is usually from 300 to
600° C., and preferably from 400 to 550° C. A calcination
time in the first calcination step is usually from 5 minutes to 40 hours,
and preferably from 1 to 20 hours.

[0025] The calcined product resulting from the first calcination is
subjected to heat treatment in the presence of a reducing material [Step
(2)] to obtain a reduced product having a mass loss of from 0.05 to 6% by
weight. Such a treatment conducted in the presence of a reducing material
will hereinafter be referred simply as a "reduction treatment". The mass
loss is defined by the following equation (I):

Mass loss(%)=[(Wa-Wb)/Wa]×100 (I)

in which Wa is a weight of a calcined product before the reduction
treatment, and Wb is a weight of a reduced product after the reduction
treatment.

[0026] Examples of the reducing material include hydrogen, ammonia, carbon
monoxide, hydrocarbons, alcohols, aldehydes and amines. Optionally, two
or more of such reducing materials may be used. Preferably, hydrocarbons,
alcohols, aldehydes and amines each have 1 to about 6 carbon atoms.
Examples of such hydrocarbons include saturated aliphatic hydrocarbons
such as methane, ethane, propane, n-butane and isobutane, unsaturated
aliphatic hydrocarbons such as ethylene, propylene, α-butylene,
β-butylene and isobutylene, and aromatic hydrocarbons such as
benzene. Examples of such alcohols include saturated aliphatic alcohols
such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl
alcohol, isobutyl alcohol, sec-butyl alcohol and tert-butyl alcohol,
unsaturated aliphatic alcohols such as allyl alcohol, crotyl alcohol and
methallyl alcohol, and aromatic alcohols such as phenol. Examples of such
aldehydes include saturated aliphatic aldehydes such as formaldehyde,
acetaldehyde, propionaldehyde, n-butylaldehyde and isobutylaldehyde, and
unsaturated aliphatic aldehydes such as acrolein, crotonaldehyde and
methacrolein. Examples of such amines include saturated aliphatic amines
such as methylamine, dimethylamine, trimethylamine, ethylamine,
diethylamine and triethylamine, and unsaturated aliphatic amines such as
allylamine and diallylamine, and aromatic amines such as aniline.

[0027] The reduction treatment is usually conducted by subjecting the
calcined product to heat treatment in an atmosphere of a gas containing
the reducing material. The concentration of the reducing material in the
gas is usually from 0.1 to 50% by volume, and preferably from 3 to 30% by
volume. The reducing material may be diluted with nitrogen, carbon
dioxide, water, helium, argon, or the like so that such a concentration
could be achieved. Molecular oxygen may be present in the reducing
atmosphere unless the effect of the reduction treatment is affected.
Preferably, no molecular oxygen is present in the reducing atmosphere.

[0028] A temperature for the reduction treatment is usually from 200 to
600° C., and preferably from 300 to 500° C. The time of the
reduction treatment is usually from 5 minutes to 20 hours and preferably
from 30 minutes to 10 hours. It is preferable to conduct the reduction
treatment by placing the calcined product in a tubular or box-shaped
container and keeping the container ventilated with a gas containing the
reducing material. At this time, a gas discharged from the container may
be circulated and reused, if necessary.

[0029] Accordingly, the reduced product having a mass loss, represented by
the above equation (I), of 0.05 to 6% by weight is obtained. The mass
loss may be attributed to the loss of lattice oxygen atoms from the
calcined product, which results in the formation of the reduced product.
Therefore, the mass loss of the calcined product may be used as an
indicator to monitor the progress of reduction. When the progress of
reduction is small, sufficient effects of the reduction may not be
attained. When the calcined product is excessively reduced, heat is
abruptly generated in the second calcination step carried out in a
molecular oxygen-containing atmosphere, which will be explained below, so
that the temperature control may become difficult. Therefore, the mass
loss of the calcined product after the reduction treatment is preferably
from 0.1 to 5% by weight.

[0030] In the reduction treatment, the reducing material itself,
decomposition products derived from the reducing material or the like may
remain in the catalyst after the reduction treatment according to the
type of the reducing material used, heat treatment conditions or the
like. In such a case, the mass loss can be calculated by measuring the
weight of the residual material in the catalyst and then calculating the
weight after the reduction treatment by subtracting the mass of the
residual material from the weight of the catalyst including the residual
material. A typical residual material is carbon and, therefore, the mass
of the residual material can be determined, for example, by total carbon
(TC) analysis.

[0031] The reduced product resulting from the reduction treatment is
secondly calcined (second calcination) in a molecular oxygen-containing
gas atmosphere [Step (3)]. The molecular oxygen concentration of the gas
is usually from 1 to 30% by volume, and preferably from 10 to 25% by
volume. Ambient air or pure oxygen is usually used as the source of
molecular oxygen. Such a source is used as a molecular oxygen-containing
gas, if necessary, after being diluted with nitrogen, carbon dioxide,
water, helium, argon, or the like. The calcination temperature in the
second calcination step is usually from 200 to 600° C., and
preferably from 350 to 550° C. The calcination time in the second
calcination step is usually from 5 minutes to 20 hours, and preferably
from 30 minutes to 10 hours.

[0032] The catalyst produced by the method of the present invention is
usually molded in a desired form before use. The catalyst may be molded
in the form of a ring, a pellet, a sphere or the like by tabletting,
extrusion molding or the like. The catalyst components may be supported
on a carrier, for example, silica, alumina, silicon carbide and silicon
nitride. In the molding, for improving the mechanical strength of the
catalyst, inorganic fiber or the like, which is substantially inert to
the intended oxidation reaction, may be added as disclosed in, for
example, JP-A-09-052053.

[0033] The present invention can increase the mechanical strength of the
catalyst by performing the second calcination. Therefore, the catalyst is
preferably molded before the second calcination. Specifically, it is
preferable to mold the dried product obtained by drying the aqueous
solution or the aqueous slurry containing the raw materials of the
catalyst, the calcined product obtained by the first calcination, or the
reduced product obtained by the reducing treatment.

[0034] Thus, the method of the present invention can improve the
mechanical strength of a catalyst for use in the production of an
unsaturated aldehyde and/or an unsaturated carboxylic acid which catalyst
comprises (or, preferably, is composed of) a mixed oxide comprising
molybdenum, bismuth and iron. Accordingly, the breakage of the catalyst
is prevented when it is filled in a reactor. As a result, it is possible
to reduce the pressure drop during the reaction, to catalytically oxidize
propylene stably with molecular oxygen in a vapor phase to stably produce
acrolein and acrylic acid, and to catalytically oxidize isobutylene or
tert-butyl alcohol stably with molecular oxygen in a vapor phase to
stably produce methacrolein and methacrylic acid.

[0035] The vapor-phase catalytic oxidation reaction is usually carried out
by filling the catalyst of the present invention in a fixed bed
multitubular reactor and feeding a raw material gas containing a raw
material compound selected from the group consisting of propylene,
isobutylene and tert-butyl alcohol, and molecular oxygen. An air is
usually used as a source of molecular oxygen. Besides the raw material
compounds and molecular oxygen, the raw material gas may optionally
contain nitrogen, carbon dioxide, carbon monoxide, water vapor and the
like.

[0036] The reaction temperature is usually from 250 to 400° C. The
reaction pressure may be reduced pressure, but it is usually from 100 to
500 kPa. The amount of molecular oxygen is usually from 1 to 3 moles per
mole of the raw material compound. The space velocity (SV) of the raw
material gas is usually from 500 to 5000/h at STP (standard temperature
and pressure, such as a temperature of 0° C. and a pressure of 100
kPa).

[0037] Examples of the present invention are shown below, but they do not
limit the present invention in any way. In the examples, the unit
"ml/min" indicating the flow rate of gas is at STP, unless otherwise
stated.

[0038] Falling Strength Test of Catalyst

[0039] A stainless steel mesh having 4.76 mm openings is fixed at the
bottom of a metal tube having an inner diameter of 30 mm and a length of
5 m and being arranged almost perpendicularly to the horizontal direction
so that the plane of the mesh is substantially horizontal. Then, X g of a
catalyst is charged from the top of the metal tube to fall. The fallen
catalyst particles are collected and placed on a sieve having 4.76 mm
openings, followed by vibration of the sieve. Then, Y g of the catalyst
particles remain on the sieve. The falling strength (%) of the catalyst
is defined as follows:

Falling strength(%)=Y/X×100(%)

[0040] In the Examples, a conversion (%) and a yield are defined as
follows:

Conversion(%)=100×[(moles of supplied isobutylene)-(moles of
unreacted isobutylene)]/(moles of supplied isobutylene)

Total yield(%)=100×(total moles of methacrolein and methacrylic
acid)/(moles of supplied isobutylene)

Example 1

(a) Preparation of Calcined Product [Step (1)]

[0041] 13,241 g of ammonium molybdate
[(NH4)6Mo.sub.7O24.4H2O] was dissolved in 15,000 g of
warm water to form Liquid A. Separately, 6,060 g of iron (III) nitrate
[Fe(NO3)3.9H2O], 13,096 g of cobalt nitrate
[Co(NO3)2.6H2O] and 585 g of cesium nitrate [CsNO3]
were dissolved in 6,000 g of warm water and subsequently 2,910 g of
bismuth nitrate [Bi(NO3)3.5H2O] was further dissolved to
form Liquid B. Liquid B was added to Liquid A while stirring to form a
slurry. The slurry was then dried with a flash dryer to obtain a dried
product. Nine (9) parts by weight of silica alumina fiber (RFC400-SL
produced by Saint-Gobain®) and 2.5 parts by weight of antimony
trioxide (Sb2O3) were added to 100 parts by weight of the dried
material. The resulting mixture was molded into a ring form having an
outer diameter of 6.3 mm, an inner diameter of 2.5 mm and a length of 6
mm, and then was calcined at 545° C. for 6 hours in an air flow to
obtain a calcined product. This calcined product contained 0.96 bismuth
atom, 2.4 iron atoms, 7.2 cobalt atoms, 0.48 cesium atom and 0.48
antimony atom per 12 molybdenum atoms.

(b) Reduction Treatment [Step (2)]

[0042] Seventy-five (75) ml of the calcined product obtained in the above
step (a) was filled in a glass tube, and then a mixed gas of
hydrogen/nitrogen (5/95 by volume) was flowed at a flow rate of 300
ml/min. through the glass tube to conduct a reduction treatment at
345° C. for 8 hours. Then, the supply of hydrogen was stopped, and
the product was cooled to room temperature while flowing the nitrogen gas
alone to obtain a reduced product. The mass loss due to the reduction
treatment was 1.04% by weight.

(c) Second Calcination [Step (3)]

[0043] The reduced product obtained in the above step (b) was calcined at
350° C. for 3 hours in an air flow to obtain Catalyst A.

(d) Falling Strength Test of Catalyst A

[0044] Thirty (30) g of Catalyst A obtained in the above step (c) was
subjected to the falling strength test described above. The falling
strength of Catalyst A was 91.8%. The result is shown in Table 1.

(e) Oxidation of Isobutylene

[0045] Into a glass reaction tube having an inner diameter of 18 mm, 14.3
ml of Catalyst A obtained in the above step (c) was filled after being
diluted with 30 g of silicon carbide (SHINANO-RUNDUM GC F16 produced by
Shinano Electric Refining Co., Ltd.). An oxidation reaction was conducted
at a reaction temperature of 360° C. by supplying a mixed gas of
isobutylene/oxygen/nitrogen/steam (1.0/2.0/10.0/2.7 by mole) into the
reaction tube at a flow rate of 157.5 ml/min. The conversion of
isobutylene and the total yield of methacrolein and methacrylic acid were
98.9% and 79.6%, respectively.

Example 2

(a) Preparation of Catalyst [Steps (1), (2) and (3)]

[0046] Catalyst B was prepared in the same manner as in the steps (a), (b)
and (c) of Example 1 except that the calcining temperature in the step
(c) of Example 1 was changed from 350° C. to 370° C.

(b) Falling Strength Test of Catalyst B

[0047] Thirty (30) g of Catalyst B obtained in the previous step (a) of
this Example was subjected to the falling strength test described above.
The falling strength of Catalyst B was 91.9%. The result is shown in
Table 1.

Example 3

(a) Preparation of Calcined Product [Step (1)]

[0048] A calcined product was prepared in the same manner as in Step (a)
of Example 1 except that the amount of the silica alumina fiber was
changed from 9 parts by weight to 12 parts by weight.

(b) Reducing Treatment [Step (2)]

[0049] A reduced product was prepared in the same manner as in Step (b) of
Example 1 except that the calcined product obtained in the previous step
(a) of this Example was used in place of the calcined product obtained in
the step (a) of Example 1. The mass loss due the reduction treatment was
1.06% by weight.

(c) Second Calcination [Step (3)]

[0050] The second calcination was carried out in the same manner as in the
step (c) of Example 1 except that the reduced product obtained in the
previous step (b) of this Example was used in place of the reduced
product obtained in the step (b) of Example 1, the calcining temperature
was changed from 350° C. to 330° C., and the calcining time
was changed from 3 hours to 5 hours. Thereby, Catalyst C was obtained.

(d) Falling Strength Test of Catalyst C

[0051] Thirty (30) g of Catalyst C obtained in the previous step (c) of
this Example was subjected to the falling strength test described above.
The falling strength of Catalyst C was 92.0%. The result is shown in
Table 1.

Example 4

(a) Preparation of Catalyst [Steps (1), (2) and (3)]

[0052] Catalyst D was prepared in the same manner as in the steps (a), (b)
and (c) of Example 3 except that the calcining temperature in the step
(c) of Example 3 was changed from 330° C. to 420° C.

(b) Falling Strength Test of Catalyst D

[0053] Thirty (30) g of Catalyst D obtained in the previous step (a) of
this Example was subjected to the falling strength test described above.
The falling strength of Catalyst D was 93.3%. The result is shown in
Table 1.

COMPARATIVE EXAMPLE 1

(a) Preparation of Catalyst [Step (1) Only]

[0054] The procedures of the step (a) of Example 1 were repeated to obtain
a calcined product, which was used as Catalyst E.

(b) Falling Strength Test of Catalyst E

[0055] Thirty (30) g of Catalyst E obtained in the previous step (a) of
this Comparative Example was subjected to the falling strength test
described above. The falling strength of Catalyst E was 86.1%. The result
is shown in Table 1.

(c) Oxidation of Isobutylene

[0056] Isobutylene was oxidized in the same manner as in the step (e) of
Example 1 except that Catalyst E obtained in the above step (a) of this
Comparative Example was used in place of Catalyst A. The conversion of
isobutylene and the total yield of methacrolein and methacrylic acid were
95.1% and 79.4%, respectively.

COMPARATIVE EXAMPLE 2

(a) Preparation of Catalyst [Steps (1) and (2) Only]

[0057] The procedures of the steps (a) and (b) of Example 1 were repeated
to obtain a reduced product, which is referred to as Catalyst F.

(b) Falling Strength Test of Catalyst F

[0058] Thirty (30) g of Catalyst E obtained in the previous step (a) of
this Comparative Example was subjected to the falling strength test
described above. The falling strength of Catalyst F was 83.8%. The result
is shown in Table 1.

COMPARATIVE EXAMPLE 3

(a) Preparation of Catalyst [Step (1) only]

[0059] The procedures of the step (a) of Example 3 were repeated to obtain
a calcined product, which was used as Catalyst G.

(b) Falling Strength Test of Catalyst G

[0060] Thirty (30) g of Catalyst G obtained in the previous step (a) of
this Comparative Example was subjected to the falling strength test
described above. The falling strength of Catalyst G was 86.4%. The result
is shown in Table 1.

COMPARATIVE EXAMPLE 4

(a) Preparation of Catalyst [Steps (1) and (2) Only]

[0061] The procedures of the steps (a) and (b) of Example 3 were repeated
to obtain a reduced product, which was used as Catalyst H.

(b) Falling Strength Test of Catalyst H

[0062] Thirty (30) g of Catalyst H obtained in the previous step (a) of
this Comparative Example was subjected to the falling strength test
described above. The falling strength of Catalyst H was 84.6%. The result
is shown in Table 1.